Concrete is used in constructing a variety of different structures such as buildings, bridges and roads. Typically concrete is prepared in the form of ready mix concrete at a central location and then transported via truck to a location where the ready mix concrete is to be used. While this technique allows larger batches of ready mix concrete to be produced, the quality of concrete varies significantly depending on the distance between location where the ready mix concrete is prepared and the location where the ready mix concrete is used as the ready mix concrete begins the curing process as soon as it is prepared. As such, it is often necessary to add components to the ready mix concrete that either slows or speeds the curing process.
In an attempt to overcome the drawbacks associated with producing ready mix concrete at a central location and then trucking the ready mix concrete to the use locations, it has been proposed to create a concrete plant that is portable such that the portable concrete plant may be transported to a location that is proximate where the ready mix concrete will be used. For example, Flood, U.S. Pat. No. 5,730,523, describes a portable concrete plant that is mounted on a single vehicle. The Flood portable concrete plant includes hoppers for storing rock, sand, cement and water. The Flood portable concrete plant also has a conveyor system that conveys the rock, sand and cement into a rotating drum where the components are mixed with water to prepare ready mix concrete. A pump is used for dispensing the ready mix concrete from the rotating drum.
Weisbrod, U.S. Pat. No. 4,298,288, discloses a portable concrete apparatus that is suited for preparing ready mix concrete proximate to a location where the concrete is to be used. The Weisbrod apparatus feeds rock, sand, cement and water at different locations along a mixing auger. Once sufficiently mixed, the ready mix concrete is pumped through a hose to the location where it is used. The Weisbrod system is particularly suited for use with preparing relatively small amounts of ready mix concrete.
One of the important components of a system that prepares ready mix concrete is the slurry mixer that mixes water, cement and other components into a slurry, which then can be mixed with rock and sand to produce the ready mix concrete. Brown et al., U.S. Pat. No. 4,588,299, and Strehlow, U.S. Pat. No. 4,865,457, each disclose a slurry mixer having a horizontally oriented mixing region.
Milek, U.S. Pat. No. 6,030,112, discloses a slurry batch mixer that has an elongated configuration. The slurry batch mixer has a trough with a curved bottom. A ribbon type screw conveyor is mounted in the trough parallel to an axis of the trough. Rotation of the screw conveyor not only mixes the components together but also conveys the mixed components to a discharge port of the trough. Williams, U.S. Pat. No. 5,718,508, discloses a self-cleaning slurry mixer having a cylindrical shape with a feed screw extending therethrough to mix together the components and to convey the mixed slurry to the slurry outlet. Macauley et al., U.S. Pat. No. 5,427,448, describes a twin screw slurry mixer where the screws are oriented parallel to each other.
Hood, U.S. Pat. No. 5,908,240, describes a tank-type slurry mixer that has two sets of paddles rotatably mounted therein. The paddles cause the mixture to be drawn in the downward direction and then flow upwardly along the side walls of the tank. Brown, U.S. Pat. No. 4,963,031, also discloses a tank-type slurry mixer. None of the prior art references or discloses a portable concrete plant that is suitable for producing ready mix concrete at rates of between 75 and 200 cubic yards per hour as is typically required for commercial applications.
Accurately controlling the flow of rock and sand also plays an important role in preparing ready mix concrete with consistent characteristics. Bush, U.S. Pat. No. 4,976,378, describes a paddle-type feed metering system. The Bush device includes four paddles that are rotatably mounted in an enclosure. Rotation of the paddle dispenses a predetermined weight of material.